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FUNCTION SEC_ORD_LEAP_ADV, B_IC=B_IC,del_t,del_x,del_y,times
ss=SIZE(B_IC.A0,/ DIMENSIONS)
A_LF2=FLTARR(times, ss[0], ss[1])

C_u = FLTARR(ss[0],ss[1])
C_v = FLTARR(ss[0],ss[1])

for i = 0, ss[0]-1 do begin
   for j = 0, ss[1]-1 do begin
      C_u[i,j] = B_IC.UU[i,j]*(del_t/del_x)
      C_v[i,j] = B_IC.VV[i,j]*(del_t/del_y)
   endfor
endfor


A_LF2(0,*,*)=  B_IC.A0(*,*)
  FOR t=0, times-2 DO BEGIN
    IF (t EQ 0) THEN BEGIN
        FU=FORWARD_UP_ADV(B_IC=B_IC,del_t,del_x,del_y,1)
        A_LF2(0,*,*)=FU(0,*,*)
    ENDIF
      FOR i=1, ss[0]-2 DO BEGIN
          FOR j=1, ss[1]-2 DO BEGIN         
              ; A_LF2(t+1,i,j)= A_LF2(t,i,j)- ((B_IC.Cu(i,j)*(A_LF2(t,i+1,j)-A_LF2(t,i-1,j))) - ((B_IC.Cv(i,j))*(A_LF2(t,i,j+1)-A_LF2(t,i,j-1))))    
                A_LF2(t+1,i,j)= A_LF2(t,i,j)- ((C_u(i,j)*(A_LF2(t,i+1,j)-A_LF2(t,i-1,j))) - ((C_v(i,j))*(A_LF2(t,i,j+1)-A_LF2(t,i,j-1))))    
          ENDFOR
      ENDFOR
  ENDFOR
  
PRINT,'>>>>>>>>>>  Sec order leap frog done'
RETURN, A_LF2

END
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